Balancing system for turbomachine rotor

ABSTRACT

The present invention relates to a turbomachine rotor balancing system ( 61 ) comprising a balancing flange ( 52 ) provided with through-passageways ( 78 ) and also comprising balance weights ( 54 ) mounted fixedly on the balancing flange by means of at least one screw/nut assembly ( 56 ) passing through one of the passageways. 
     According to the invention, for each of the passageways ( 78 ), the flange ( 52 ) has on its first face ( 90 ) a first recess ( 94 ) passing via the radial summit ( 80 ) of the passageway, this first recess being deprived of contact with the screw head ( 86 ) pressing on this face ( 90 ), the flange ( 52 ) having on its second face ( 92 ) a second recess ( 98 ) passing via the radial summit ( 80 ), this second recess being deprived of contact with the balance weight ( 54 ) pressing on this face ( 92 ).

BACKGROUND OF THE INVENTION

The present invention relates in a general manner to a turbomachinerotor balancing system and to a turbomachine module comprising at leastone such balancing system.

The invention also relates to a turbomachine fitted with at least onesuch module, the turbomachine preferably taking the form of a turbojetfor an aircraft.

DESCRIPTION OF THE PRIOR ART

On existing turbomachine modules, such as compressors or turbines, arotor balancing system is usually provided comprising an annularbalancing flange on which balance weights are mounted with the aid ofbolts housed in through-passageways of the annular flange. The weightsmay therefore be distributed around the flange in the desired manner,providing a good balancing of the associated turbomachine module.Accordingly, this type of rotor balancing system is usually qualified asmodular.

More precisely, the annular balancing flange usually comprises anannular core delimited radially in a first direction by a junction zonefrom which extends radially in this first direction a plurality ofthrough-passageways, toward a radial free flange end, eachthrough-passageway having a radial summit, in a second directionopposite to the first direction, belonging to said junction zone.Usually, the first direction is the one going radially inward, and thesecond opposite direction is the one going radially outward.

In addition, the system therefore comprises a plurality of balanceweights mounted fixedly on the annular balancing flange by means of atleast one screw/nut assembly passing through one of the passageways, thescrew head pressing against a first face of the annular balancing flangeand the balance weight pressing against a second face of the annularbalancing flange, opposite to the first face.

During studies carried out in the context of determining the stressessustained by the balancing flange, it has been noted that the highesttangential stresses were located at the radial summit of eachthrough-passageway, hence on or close to the aforementioned junctionzone. As an indication, it is specified that the tangential stresses areessentially linked to the centrifugal or thermal effects.

In addition, it is noted that the portions of the balancing flange thatare highly tangentially stressed are also axially stressed by theclamping of the screw/nut assembly. Therefore, the combination of thesetangential and axial stresses may lead to too short a service life ofthe balancing flange, and furthermore generate major risks of damagingthis flange.

SUMMARY OF THE INVENTION

The object of the invention is therefore to propose a turbomachine rotorbalancing system and a turbomachine module remedying the abovementioneddisadvantages relating to the embodiments of the prior art.

To do this, the subject of the invention is first of all a turbomachinerotor balancing system comprising an annular balancing flange providedwith an annular core delimited radially in a first direction by ajunction zone from which a plurality of through-passageways extendsradially in the first direction toward a radial free flange end, eachthrough-passageway having a radial summit, in a second directionopposite to the first direction, belonging to the junction zone, thesystem also comprising a plurality of balance weights fixedly mountedonto the annular balancing flange by means of at least one screw/nutassembly passing through one of the passageways, one of the elementsheld between the nut and the screw head pressing against a first face ofthe annular balancing flange and the balance weight pressing against asecond face of the annular balancing flange, opposite to the first face.

According to the invention, for each of the through-passageways, theannular balancing flange has on its first face a first recess passingvia the radial summit and extending on either side of the junction zone,this first recess being deprived of contact with the element heldbetween the nut and the screw head, the balancing flange having, on itssecond face, a second recess passing via the radial summit and extendingon either side of the junction zone, this second recess being deprivedof contact with the balance weight.

Therefore, the invention proposes a clever solution making it possibleto transfer the axial stresses arising from the clamping of thescrew/nut assembly away from the zone of the annular balancing flangethat is furthermore put under great strain by the tangential stresses,this zone, as mentioned above, being centered on the radial summit ofthe through-passageway concerned.

Specifically, the recesses provided are therefore made so as to openinto the associated through-passageways, while making these recesses oneither side of said junction zone, namely jointly on the annular core ofthe flange and on the portion called pierced, also annular andincorporating the various through-passageways. In this manner, for eachof the through-passageways, said element held between the nut and thescrew head is no longer pressing against the radial summit from which itis separated by a distance equal to the depth of the first recess, whichmakes it possible to generate virtually no axial stress on this summitthat is put under great tangential strain by the centrifugal and thermaleffects.

Consequently, the decoupling of the tangential and axial stresses thatis achieved in the present invention advantageously leads to increasingthe service life of the balancing flanges, and also greatly limits therisks of damage to the latter.

It is indicated that the invention provides that each recess is situatedaround the associated through-passageway, on and close to the radialsummit. Naturally, the recess concerned, also able to be likened to anotch or a back-off, could extend to a greater extent around thepassageway, and even completely around the latter, without departingfrom the context of the invention.

Finally, the annular balancing flange may without distinction bedesigned to be fixedly attached to a rotor disk, in particular to itsbore definition enlarged inner radial portion, also called a “leek”, orelse to be indistinguishable from any connecting flange forming anintegral part of the associated turbomachine module.

Preferably, in cross section of the flange passing via thethrough-passageways, the junction zone takes the form of a circlecentered on an axis of the annular flange.

In addition, still in cross section of the annular flange passing viathe through-passageways, the radial summit of each through-passagewaypreferably takes the form of a point belonging to the circle centered onthe axis of the annular flange.

Preferably, the first recesses consist of a single circular groove madeon the first face, in a centered manner on the axis of the annularflange, and the second recesses consist of a single circular groove madeon the second face, also in a centered manner on the axis of the annularflange. This solution is advantageous in the sense that it makes itpossible, with the aid of a simple and single machining operation of oneof the faces of the annular balancing flange, to obtain all the recessesof this face.

Again preferably, each balance weight is fitted to the balancing flangeby means of two screw/nut assemblies passing respectively through two ofthe passageways that are directly consecutive.

In addition, provision is preferably made, for each through-passageway,for the screw head to press against the first face of the balancingflange, the nut then pressing against the balance weight. Naturally, itwould be possible to provide a reverse situation in which the nut ispressing against the first face of the balancing flange and the screwhead pressing against the balance weight, without departing from thecontext of the invention.

Finally, each through-passageway takes the form of a scallop or a hole.As an indication, the scallop is conventionally radially open in thefirst direction, namely opening at said radial free flange end, whilethe hole for its part has a closed section.

Also, a further subject of the invention is a turbomachine modulecomprising at least one rotor balancing system as explained above.

Preferably, the module is a turbine or high pressure or low pressureturbomachine compressor.

Finally, another subject of the invention is a turbomachine such as anaircraft turbojet comprising at least one module as described above.

Other advantages and features of the invention will appear in thenonlimiting description detailed below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with respect to the appended drawingsamongst which:

FIG. 1 represents a partial side view of a turbomachine module accordingto a preferred embodiment of the present invention;

FIG. 2 shows a partial view in perspective of the annular balancingflange designed to form an integral part of the rotor balancing systembelonging to the turbomachine module shown in FIG. 1;

FIG. 3 shows a view in section along the line III-III of FIG. 2, towhich a balance weight and its associated assembly means have beenadded;

FIG. 4 shows a view in section along the line IV-IV of FIG. 3; and

FIG. 5 shows a partial view in section along the line V-V of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a portion of a turbomachine module 1 according to apreferred embodiment of the present invention, this module here being ahigh pressure turbine called an HP turbine of the turbomachine, taking,for its part, the form of a turbojet for an aircraft.

In FIG. 1, the rotor portion of the HP turbine can be seen situateddownstream of a combustion chamber 2 of the turbojet. In this respect,it is noted that the concepts “downstream” and “upstream” employed beloware to be considered in relation to a main direction of flow of thegases through the turbomachine, indicated schematically by the arrow 4,this direction being substantially parallel to a longitudinal axis 6 ofthe turbojet corresponding simultaneously to an axis of the module 1 andof the disks comprising it.

Specifically, the module 1 comprises a main rotor disk called the bladesupport disk 8, with an axis 6 passing through a system of axes 10 ofthe turbojet thanks to the presence of a bore 12. More precisely, thisbore 12 is made in a known manner at an enlarged inner radial portion14, forming the thickest portion of the disk 8, and delimited by anupstream face 16 and a downstream face 18 both orthogonal to the axis 6.The enlarged inner radial portion 14, also called the “leek”, thereforehas a substantially constant thickness in the direction of the axis 6,that is equal to the length of the bore 12 in this same direction.

At an outer radial end portion 20 of the disk 8 turbine blades 22 aremounted through which the gases escaping from the combustion chamber 2can expand.

On the downstream side 23 of the blade support disk 8 a connectingannular flange 24 is arranged that is used for attaching this disk 8 toa downstream portion of the module, not shown. As can be seen in FIG. 1,the downstream annular connecting flange 24 protrudes from thedownstream side 23 with which it is made in a single piece, at a portionsituated above the enlarged inner radial portion 14.

On the other hand, on the upstream side 26 of the blade support disk 8another annular connecting flange 28 is arranged that is used to attachthis disk 8 to another turbomachine module, and more specifically to thehigh pressure compressor, called the HP compressor (not shown),comprising for its part a downstream connecting annular flange 30. Hereagain, as can be seen in FIG. 1, the upstream connecting annular flange28 protrudes from the upstream side 26 with which it is made in a singlepiece, at a portion situated above the enlarged inner radial portion 14.

Also, in addition to the function of assembly with the HP compressor,this upstream connecting annular flange 28 is also used for the mountingof a labyrinth disk 32 situated upstream of the blade support disk 8,whose main function known to those skilled in the art resides in helpingto cool this disk 8 and the blades that it supports. Specifically, thedisk 32, comprising one or more annular sealing devices of the labyrinthtype 34 lying tangentially to the stator of the module, makes itpossible to define an annular cooling space 36 toward the downstream,between itself and the disk 8 to be cooled. Therefore, the cool airentering this space 36 closely follows the upstream side 26 of the disk8, before rejoining radially outward a circuit of air through the blades22, as shown schematically by the arrow 38 of FIG. 1.

In this preferred embodiment of the present invention, the labyrinthdisk 32 is arranged between the two annular connecting flanges 28, 30,on which it is fixedly mounted with the aid of bolts 40 used to assemblethe two flanges, and distributed about the axis 6.

The labyrinth disk 32 also passes through the system of axes 10 of theturbojet, thanks to the presence of a bore 44. More precisely, this bore44 is made in a known manner at an enlarged inner radial portion 46,constituting the thickest portion of the disk 32 and delimited by anupstream face 48 and a downstream face 50 both orthogonal to the axis 6.The enlarged inner radial portion 46, also called the “leek”, thereforehas a substantially constant thickness in the direction of the axis 6,that is equal to the length of the bore 44 in this same direction.

In this preferred embodiment, an annular balancing flange 52 isarranged, fitted with balance weights 54, on the enlarged inner radialportion 46. More precisely, this annular balancing flange 52 is made ina single piece with the enlarged inner radial portion 46 from which itprotrudes upstream then radially inward, from the face 48. In a generalmanner, the flange 52 and the weights 54 being fitted thereto in adetermined manner together form a turbomachine rotor balancing system61.

Since this balancing flange 52 is separate from the connecting flangesindicated above, the balance weights 54 may then be mounted definitivelyon this flange 52 before the operation of joining the module 1 withanother turbomachine module. The manufacturer of such a turbomachinemodule 1 is consequently able to ensure a satisfactory installation ofthe balancing system, in particular of the weights 54 on the flange 52with the aid of bolts 56, because the subsequent assembly of this samemodule 1 with another turbomachine module, in this instance the HPcompressor, does not require any disassembly/assembly of the balanceweights already installed on the flange 52 provided for this purpose.

As can be seen in FIG. 1, it can be arranged for the balancing flange 52to protrude upstream from the face 48 at the outer radial end of thelatter, namely at the intersection of this face 48 orthogonal to theaxis 6 with the rest of an upstream side 58 of this disk 32, opposite toa downstream side 60 delimiting the cooling space 36.

Consequently, it must be understood that the balancing flange 52 isdeprived of a function of connection with another element of theturbomachine, whether it be an element of the same module 1 or of anadjacent module of the turbomachine, which means that its functionresides only in supporting the balance weights 54. Therefore, no elementof the turbomachine other than the balance weights 54 is attached tothis annular balancing flange 52, which, as can be seen in FIG. 1, isplaced radially internally relative to the aforementioned connectingannular flanges 28, 30 used for the connection of the HP turbine to theHP compressor, and for the support of the labyrinth disk 32.

Now with reference to FIGS. 2 to 4, one of the particular features ofthe present invention, residing in the particular design of the annularbalancing flange 52 with the axis 6, also called the axis of the annularflange, can be seen.

The annular balancing flange 52 essentially comprises two portions thatare adjacent and offset in a radial direction 62 of the flange, namelyan annular core 64 forming the outer radial portion of this flange, anda pierced portion 66 forming the inner radial portion of the latter. Thecore 64, or main portion of the flange 52, is solid and incorporates anannular connecting portion 68 providing the connection of the flange tothe face 48 of the enlarged inner radial portion 46 of the disk 32.

The core 64 therefore extends in the radial direction 62 in a firstdirection 70 corresponding to the inward direction, to a zone called thejunction zone schematized by the dashed lines 74 and separating thiscore 64 from the pierced portion 66, the junction zone 74 preferablytaking the form of a fictional cylinder of circular section centered onthe axis 6. Note that the second direction 72 associated with the radialdirection 62 and shown in the figures corresponds to the outwarddirection.

The annular pierced portion 66 therefore extends radially from thejunction zone 74, in the first direction 70, up to a radial free flangeend 76. This portion 66 therefore incorporates through-passageways 78that each extend radially from the junction zone 74, in the firstdirection 70 toward the radial free flange end 76. Here, the passageways78 take the form of scallops, namely they extend radially over the wholeannular pierced portion 66, since they open radially inward at theradial free flange end 76. In other words, they each have an opencontour, unlike a hole having a closed contour. Accordingly, thepassageways 78 could alternatively take the form of a hole, withoutdeparting from the context of the present invention.

In addition, it is indicated that each through-passageway 78 has aradial summit 80 in the second direction 72, a summit that belongs tothe aforementioned junction zone 74.

More precisely, with reference to FIG. 4, it can be seen that thepassageways 78 used for the bolts 56 to pass through all havesubstantially identical shape and dimensions, so that, in cross sectionof the flange passing through these through-passageways 78, or else inthe view in cross section of this FIG. 4, the junction zone 74 takes theform of a circle centered on the axis 6. In addition, it can be seenthat the radial summit 80 of each through-passageway 78 takes the formof a point belonging to the circle 74, because the bottom of each of thescallops 78 preferably has a slight curvature oriented radially inward,in the first direction 70. In this respect, it is specified, as shown inFIG. 3, similar to a diametral or radial section, that this radialsummit 80 takes in this section the form of a right-hand segmentpreferably parallel to the axis 6 (not shown) and extending over thewhole length of the passageway 78 in the direction of this same axis. Inaddition, this same right-hand segment 80 belongs entirely to thejunction zone 74.

FIG. 3 shows that the balance weights 54 (only one being visible in FIG.3) are fixedly mounted onto the balancing flange 52 by means of one ormore screw/nut assemblies 56 each passing through one of the passageways78, each weight 54 preferably being fitted to the flange 52 with the aidof two screw/nut assemblies 56 passing respectively through two directlyconsecutive passageways 78 in the tangential direction of the flange 52,as will be detailed later.

In addition, the assembly 56 therefore comprises a screw 84 having ascrew head 86 pressing against a first face 90 or downstream face of theflange 52, substantially orthogonal to the axis 6 and facing the face 48of the labyrinth disk 32. The assembly also comprises a nut 88 mountedon a threaded portion of the screw, and this nut 88 pressing against anouter face of the associated weight 54, of which one internal face isfor its part pressing against a second face 92 or upstream face of theflange 52, substantially orthogonal to the axis 6 and opposite to thefirst face 90.

Therefore, from upstream to downstream, a stack of the nut 88, theweight 54, the flange 52 and finally the screw head 86 is provided,these elements preferably being in contact two by two.

As is shown in FIGS. 2 to 4, to prevent overstressing the flange 52 ateach passageway radial summit 80, it is proposed to transfer the axialstresses due to the clamping of the screw/nut assembly 56 passingthrough the passageway in question, by making judiciously positionedrecesses.

Effectively, for each of the scallops 78, the balancing flange 52 has,on its first face 90, a first recess 94 passing via the radial summit 80that is under great tangential stress, and extending along the junctionzone 74, and radially on either side of the latter. In other words, therecess 94 extends both to the annular core 64 and the pierced portion 66so that it can then be considered that it opens into the scallop 78concerned. As shown in FIG. 3, the first recess 94 being deprived ofcontact with the screw head 86, the pressure of the latter on thebalancing flange 52 is therefore applied to the first face 90 at adistance from the radial summit 80 that is under great tangentialstress, which makes it possible to apply virtually no axial stress atthis same summit 80. The axial stress applied to the flange 52 and dueto the clamping of the assembly 56 is therefore advantageouslytransferred radially in the second direction 72, to the heart of theannular core 64 against which the screw head 86 is pressing.

As an indication, the recess 94 is preferably made sufficiently deeplyin the first direction 70, so as to cover the totality of the curvedbottom of the scallop 78. Therefore, by continuing in this same firstdirection 70, the screw head 86 can find contact with the contour of thescallop 78, contrary to what is sought around the zone of the radialsummit 80.

For reasons of ease of manufacture and as can be best seen in FIG. 4,the first recesses 94 preferably consist of a single circular groove 96made on the first face 90, this groove 96, preferably of semicircularsection, being centered on the axis 6 and along the junction zone 74 inthe form of a circle.

In a similar manner that will be described in less detail below, thebalancing flange 52 also has on its second face 92, for each scallop 78,a second recess 98 passing through its radial summit 80 and extending oneither side of the junction zone 74, this second recess 98 beingdeprived of contact with the balance weight 52. Here again, the totalityof the second recesses 98 of the face 92 may be achieved by a singlecircular groove 99 made on this second face 92, this groove 99,preferably of semicircular section, being centered on the axis 6 andalong the junction zone 74 in the form of a circle. In a general manner,there is a similarity between the first recesses 94 and the secondrecesses 98 because the latter are preferably symmetrical relative to agiven transverse plane.

As shown in FIG. 3, each second recess 98 being deprived of contact withthe weight 54, the pressure of the latter on the balancing flange 52 istherefore applied to the second face 92 at a distance from the radialsummit 80 that is greatly stressed tangentially, which makes it possibleto apply virtually no axial stress at this same summit 80. The axialstress applied to the flange 52 and due to the clamping of the assembly56 is therefore advantageously transferred radially in the seconddirection 72, to the heart of the annular core 64 against which thescrew head 86 is pressing.

Now with reference to FIG. 5, showing another particular feature thatcan be combined with the production of the recesses described above withreference to FIGS. 2 to 4, it can be seen that each weight 54 (only onebeing shown schematically in dashed lines) is mounted fixedly onto thebalancing flange 52 with the aid of two screw/nut assemblies.

Effectively, a first screw/nut assembly referenced 56 a is providedcomprising a first screw 84 passing through a first passageway 78, and asecond screw/nut assembly referenced 56 b also comprising a second screw84 passing through a second passageway 78, offset from the firstpassageway 78 in a first direction 104 of the tangential direction 102,this first direction 104 opposite to a second direction 106corresponding therefore to the clockwise direction in FIG. 5.

As is schematized for the second passageway 78 taking the form of ascallop, while being applicable to all the through-passageways 78, it isnoted that in cross section of the flange passing through thesethrough-passageways 78, or else in the view in cross section of FIG. 5,a radial end portion 108 of the passageway in question in the seconddirection 72 consists of an arc of a circle 110 of radius R1, on eitherside of which there are two arcs of a circle 112 of radius R2 that issmaller than the radius R1. More precisely, the arc of a circle 110forms the major part of this radial end portion 108, and incorporates inits center the aforementioned radial summit 80. Also, the radius R1 ofthe two arcs of a circle 112 that delimit the radial end portion 108 issubstantially identical to the radius of the screw 84, which makes itpossible if necessary to obtain a surface contact between the screw 84and one of these two arcs of a circle 112.

Preferably, the scallop 78 has an axis of symmetry 114 extendingradially, that is to say in the direction 62, this axis of symmetry 114therefore passing through the disk axis 6 and the radial summit 80.Consequently, the two arcs of a circle 112 are therefore symmetricalrelative to the axis 114, and may each form an integral part of atangential end side of the passageway.

In this respect, each of the two passageways 78 has a first tangentialend side 116, preferably initiated at the junction between the centralarc of a circle 110 and the arc of a circle 112 situated nearest to theend in the second direction 106, and that continues in a known mannerfor a flat portion that is substantially straight and parallel to theradial direction 62 and to the axis of symmetry 114, up to the radialfree flange end 76. In a similar manner, each of the two passageways 78has a second tangential end side 118, preferably initiated at thejunction between the central arc of a circle 110 and the arc of a circle112 situated nearest the end in the first direction 104, and thatcontinues also via a flat portion that is substantially straight andparallel to the radial direction 62 and to the axis of symmetry 114, upto the radial free flange end 76.

One of the particular features of this configuration resides inproviding each screw 84 to be of smaller diameter than the tangentialwidth of the scallop 78 that it passes through, so that the radial endportion 108 extends over a great tangential distance making it possibleto reduce the concentration of stresses on and close to the radialsummit 80, particularly thanks to its evolutive and softened shape.Accordingly, it is therefore provided that a maximum tangential distanceD between the two tangential end sides 116, 118, corresponding to theconstant distance between the two flat portions of these sides 116, 118,is greater than a maximum tangential length d of said screw 84substantially identical to the value of the diameter of the latter, theratio D/d lying between 1.2 and 2, and preferably close to 1.5.

In addition, to ensure the tangential retention of the weight 54 on thebalancing flange 52, provision is first of all made for the first screw84 of the first assembly 56 a to be pressing against the firsttangential end side 116 of the first through-passageway 78, and moreprecisely pressing and in contact against the flat portion of this side116, close to the junction with the arc of a circle 112 as shown in FIG.5. Therefore, the screw is no longer in contact with this arc of acircle 112, nor in contact with the central arc of a circle 110incorporating the radial summit 80. Furthermore, because of theparticular dimensioning of the various elements above, the first screw84 is therefore situated at a distance from the second tangential endside 118 from which it is tangentially offset in the second direction106. This arrangement naturally makes it possible to hold the weight 54traversed virtually without clearance by the screw 84, in the seconddirection 106 relative to the flange 52.

Similarly, provision is also made for the second screw 84 of the secondassembly 56 b to rest against the second tangential end side 118 of thesecond through-passageway 78, and more precisely pressing and in contactagainst the flat portion of this side 118, close to the junction withthe arc of a circle 112 as shown in FIG. 5. Therefore, the screw is nolonger in contact with this arc of a circle 112, nor in contact with thecentral arc of a circle 110 incorporating the radial summit 80.Furthermore, again because of the particular dimensioning of the variouselements above, the second screw 84 is therefore situated at a distancefrom the first tangential end side 116 from which it is tangentiallyoffset in the first direction 104. This arrangement naturally makes itpossible to hold the weight 54, also traversed virtually withoutclearance by the second screw 84, in the first direction 104 relative tothe flange 52.

Finally, in order to translate the “off-center” positioning of thescrews 84 in their respective passageways, it can be seen in FIG. 5 thata screw axis 120 of the first screw is tangentially offset in the seconddirection 106 relative to the axis of symmetry 114 of the firstpassageway, while a screw axis 120 of the second screw 84 istangentially offset in the first direction 104 relative to the axis ofsymmetry 114 of the second passageway.

Naturally, various modifications may be made by those skilled in the artto the invention that has just been described, only as nonlimitingexamples. Accordingly, it is noted that, although the preferredembodiments have been described and represented with through-passagewaystaking the form of scallops, these passageways may alternatively be madewith the aid of simple holes through the balancing flange, withoutdeparting from the context of the invention.

1. A turbomachine rotor balancing system comprising a balancing flangeprovided with an annular core delimited radially in a first direction bya junction zone from which a plurality of through-passageways extendsradially in said first direction toward a radial free flange end, eachthrough-passageway having a radial summit, in a second directionopposite to said first direction, belonging to said junction zone, saidsystem also comprising a plurality of balance weights fixedly mountedonto said balancing flange by means of at least one screw/nut assemblypassing through one of said passageways, one of said elements heldbetween the nut and the screw head pressing against a first face of saidbalancing flange and said balance weight pressing against a second faceof said balancing flange, opposite to the first face, wherein, for eachof said through-passageways, said balancing flange has on its first facea first recess passing via said radial summit and extending on eitherside of said junction zone, this first recess being deprived of contactwith said element held between the nut and the screw head, saidbalancing flange having, on its second face, a second recess passing viasaid radial summit and extending on either side of said junction zone,this second recess being deprived of contact with said balance weight.2. The balancing system as claimed in claim 1, wherein, in cross sectionof the flange passing via said through-passageways, said junction zonetakes the form of a circle centered on an axis of the annular flange. 3.The balancing system as claimed in claim 2, wherein, in cross section ofthe flange passing via said through-passageways, said radial summit ofeach through-passageway takes the form of a point belonging to saidcircle centered on the axis of the annular flange.
 4. The balancingsystem as claimed in claim 2 or claim 3, wherein said first recessesconsist of a single circular groove made on said first face, in acentered manner on the axis of the annular flange, and wherein thesecond recesses consist of a single circular groove made on said secondface, in a centered manner on the axis of the annular flange.
 5. Thebalancing system as claimed in any one of the preceding claims, whereineach balance weight is fitted to said balancing flange by means of twoscrew/nut assemblies passing respectively through two of saidpassageways that are directly consecutive.
 6. The balancing system asclaimed in any one of the preceding claims, wherein, for eachthrough-passageway, said screw head is pressing against the first faceof said balancing flange and wherein said nut is pressing against saidbalance weight.
 7. The balancing system as claimed in any one of thepreceding claims, wherein each through-passageway takes the form of ascallop or a hole.
 8. A turbomachine module which comprises at least onebalancing system as claimed in any one of the preceding claims.
 9. Theturbomachine module as claimed in claim 8, which is a turbine or aturbomachine compressor.
 10. A turbomachine comprising at least onemodule as claimed in claim 8 or claim 9.